In typical gas turbine engine start systems, a start sequence may be used to coordinate engine speed, ignition, and fuel delivery mechanism to achieve a reliable start. In particular, successful engine start may be obtained within a given range of fuel/air (FAR) ratio capable of sustaining combustion in the engine. As air flow within the engine is a consequence of compressor rotational speed, an appropriate amount of fuel should be sent to the engine combustor at an appropriate speed, i.e. engine speed and fuel delivery should be coordinated, in order to create the proper FAR condition.
Manifold priming however delays the flow of fuel out of the engine's fuel manifold. On the one hand, if the engine has high acceleration and the manifold is not quickly primed, the fuel may be sent to the engine's combustor too late. This may result in an excessively poor fuel/air mixture, which may be too lean to produce engine light-up. On the other hand, if the engine has low acceleration, the fuel manifold is likely to be primed more quickly. The fuel may be sent to the engine combustor too quickly, resulting in an excessively rich mixture. In this case, although light-up is likely to be produced, extreme temperature and flames may result, leading to accelerated engine deterioration.
There is therefore a need for an improved system and method for filling an engine fuel manifold.